Aromatic polymers such as polysulfone, polyethersulfone, poly(phthalazine ether sulfone ketone), poly(p-phenylene sulfide), polyether imide, polyimide, polyphenylene oxide, polyphenylene ether, and polyether ether ketone are useful for preparing porous membranes due to their chemical stability, processability, mechanical strength, flexibility, and thermal stability. Since these polymers are generally hydrophobic, membranes prepared from these polymers are hydrophobic, and thus lack desirable surface properties such as wettability, low protein adsorption, thromboresistance, and controlled surface chemical reactivity.
Attempts have been made to improve one or more of the surface properties of membranes made from the aromatic polymers. For example, membranes have been treated with high energy radiation or plasma to impart hydrophilicity. In other examples, hydrophilic monomers have been grafted to hydrophobic membrane surfaces. Attempts also have been made to coat the hydrophobic membrane with water soluble polymers such as polyethylene glycol or polyvinyl pyrrolidone. The above attempts for improving properties, particularly hydrophilicity, however, have one or more drawbacks such as lack of reproducibility, lack of stability of the modification, and/or pore clogging.
The foregoing shows that there is an unmet need for hydrophilic membranes formed from aromatic hydrophobic polymers and for a method of imparting hydrophilicity to membranes formed from aromatic hydrophobic polymers.